This invention relates to a characteristic testing method for variable capacitance diodes, and more particularly, to a method used as an inspection method at the time of shipping or forwarding diode elements to which taping is implemented.
Variable capacitance diodes (hereinafter also abbreviated as elements) are used in place of double, triple, or quadruple mechanical variable capacitors for the receiver tuner of televisions, or radio receivers. For one tuner, two to four variable capacitance diodes are necessarily used. These elements are required to have voltage versus capacitance characteristics uniform with each other (such that they can be paired with each other). Further, for reasons of customer's work, e.g., sixty (60) elements or more having the uniform characteristics are put together (which will be called pairing) into one block. Ordinarily, several blocks per each reel, e.g., 3000 diodes are forwarded in a form when they are to be subjected to taping.
Generally, several thousand variable capacitance diode pellets are formed on a single wafer.
A conventional method of pair-sorting a plurality of elements (e.g., several thousand) will now be described with reference to FIGS. 1 and 2. In FIG. 1, the abscissa represents voltage, and the ordinate represents capacitance. In this figure, longitudinal line segments a.sub.1, a.sub.2, a.sub.3 and a.sub.4 represent capacitance distributions of the plurality of elements at voltages V.sub.1, V.sub.2, V.sub.3 and V.sub.4, respectively. The capacitance range of elements to be paired is ordinarily limited to 1 to 3%. For example, in the case where the capacitance is limited to 2%, limits are provided for every capacitance range of 2%, and line segments a.sub.1 to a.sub.4 are divided into approximately eight to ten sections, respectively. The numerals attached to the longitudinal line segments indicate section Nos., respectively. Combinations are prepared by the sections at respective voltages to attach sorting Nos. to those combinations. For example, the combination of the sorting No. A is (6-6-4-1), the combination of the sorting No. B is (1-2-5), and the combination of the sorting No. C is (3--4--8--8). Since the polygonal line zone A connecting two adjacent two section limits (the same reference numerals as those of the sorting Nos. are used for reasons of convenience) represents a voltage versus capacitance characteristic group having the uniform characteristics where the capacitance range is approximately 2% or less, elements belonging to such combinations can be paired.
When a new combination occurs while accommodating elements having the same sorting Nos. into the same bottles, respectively, that sorting No. is registered with respect to a new bottle to continue sorting. In accordance with such a method, sorting is conducted into about 500 groups at the maximum. Further, in the case of conducting shipping in the form of a taping reel, since one reel is comprised of 3000 diodes, elements which have undergone bottle sorting are subjected to taping in order from the bottle having main elements therein so that respective reels have 3000 elements.
Explanation will be given in more detail with reference to FIG. 2. Initially, 40 plastic molded elements placed on a frame 21 are separately cut off and are arranged for a second time by means of a parts feeder 22 to measure capacitance values every respective voltages (V.sub.1 to V.sub.4) by means of a characteristic measurement device 23 to determine bottles 26 with respect to respective combinations by means of a controller 24 to accommodate them into bottles of corresponding sorts by means of a sorter 25. Further, in the case of attempting to carry out taping, although not shown, elements are arranged for a second time by using the parts feeder from the bottle having many bottles therein, and are then subjected to taping. FIG. 3 is a graph in which the arrangement position of elements on the tape and the element capacitance (e.g., at 14 volts) are shown on the abscissa and the ordinate, respectively In this figure, b.sub.1, b.sub.2 and b.sub.3 represent the sorting Nos. of bottles. All these elements have the capacitance range of 2% or less and have characteristics such that those of 60 elements or more are in harmony with each other.
However, the above-mentioned conventional method has the follows problems.
(1) A special handler (sorter) capable of conducting sorting in a broad range is required, resulting in a high cost of installation.
(2) Since sorting is conducted even into approximately 500 groups, there may occur wastefulness in the space, the labor and the time for management of the product. Further, there is the possibility that elements of any different group may be mixed because of an error in handling.
(3) Ordinarily, the taping reel is comprised of 3000 elements, but there exists the limitation that, e.g., sixty elements or more must be included within each block. Accordingly, elements belonging to bottles including 60 elements or less Cannot be subjected to taping. Namely, products belonging to bottles including elements or less can be only forwarded in the form of bagging. For this reason, balance between products to be subjected to taping and products subjected to bagging is required.
(4) Since elements belonging to a bottle including two elements or less are considered to be an inferior good as the result of bottle-sorting, yield becomes poor.
(5) Since elements are sorted twice using the parts feeder, products may be deteriorated.
As described above, in the case of variable capacitance diodes, elements having voltage versus capacitance characteristic curves in harmony with each other are put together as one block (group). Thus, products are forwarded with a plurality of blocks being attached on each taping reel. In the conventional art, since sorting is conducted into groups of even 500, not only there results increased wastefulness in the installation, space, labor, and time, etc. for inspection or sorting, but also there occurs taping reel products and products subjected to bagging, disadvantageously resulting in low productivity. On the other hand, the capacitance characteristic distribution of elements irregularly varies depending on lots, and location within the wafer. However, the conventional method cannot flexibly cope with such a characteristic distribution change.